This invention relates to a lead bearing an electrode for electrically connecting an organ inside a living animal body to an electrical device. Notwithstanding its various uses, this invention will be described for purposes of this description for use as an endocardial pacing and sensing lead for connecting an artificial cardiac pacemaker to cardiac tissue.
There are generally two types of body-implantable leads used with cardiac pacemakers -- one which requires surgery to expose the myocardial tissue to which the electrode is in some manner or another affixed and another in which a lead with an electrode or electrodes located at its distal end is inserted in and guided through a body vessel such as a vein into the heart where the electrodes contact, and in some cases are secured to the heart through the endothelial tissue lining the inside of the heart. The former leads are generally referred to as myocardial type leads while the latter are generally referred to as endocardial type leads. Examples of prior myocardial leads may be found in U.S. Pat. No. 3,216,424, 3,416,534, 3,472,234, and 3,737,579. Examples of prior art endocardial leads may be found in U.S. Pat. No. 3,348,548, 3,754,555, 3,814,104, 3,844,292, and 3,974,834 and in publications such as "New Pacemaker Electrodes" by Max Schaldach appearing in Vol. 17 Transactions: American Society for Artificial Internal Organs, 1971, pp. 29-35; German Offenlegungsschrift No. 2,516,848 entitled "Transvenous Stimulation Electrode for Heart Pacemakers" published Oct. 28, 1976; and German Offenlegungsschrift No. 2,539,553 entitled "Electrode Assembly for Medical Purposes" published Mar. 10, 1977. These prior art teachings relate to various types of endocardial leads which are simple to manufacture and importantly are relatively easy to use by the implanting physician. The attributes of an endocardial lead which are most desirable are that the electrode be capable of being firmly secured into the wall of the cardiac tissue to prevent dislodgement while avoiding perforation of the electrode all the way through the cardiac tissue. In addition, it is important that the means used to secure the lead to the cardiac tissue be protected from causing damage to the vein, heart valve, or other tissue through which the lead is inserted into the heart. Other features of importance include electrodes having the desired shape and surface area requirements and means for securing the electrode to the heart without applying any permanent twisting or torque to the lead which will cause it to be stressed while in chronic use. Another problem with prior art leads has been that it is difficult to know exactly to what extent the means for securing the electrode to the cardiac tissue has been successfully achieved when the lead is in its final placement. Still another concern is, whether once in place, the electrode and/or securing means can be totally withdrawn out of the vein or at least disengaged from cardiac tissue and appropriately repositioned. The above cited prior art references have attempted with varying degrees of success to provide endocardial leads having some of the desirable features without any of the attendant problems or undesirable characteristics as described above.
The body-implantable lead of the present invention provides those features most desirable in an endocardial lead without those undesirable problems or characteristics. The present invention provides a body-implantable lead in which the electrode is of the desirable ring type having a desired shape and surface area. The electrode is a substantially elongated member having an opening passing therethrough in which is partially housed a helix. While the lead is being inserted and guided through the vein to the heart, the portion of the helix which extends out of the distal end of the electrode is prevented from causing any injury or damage to the vein, valve, or other tissues. Once in the desired location and position in the heart, the lead may be rotated so that the helix may very simply be screwed into the heart through the endocardial tissue. The helix once secured in place serves to hold the ring electrode in firm engagement with the cardiac tissue for providing the desired electrical stimulation as well as the detection to electrical signals from the heart. In the preferred embodiment the helix is electrically insulated from the electrode so that it serves only to secure the electrode in firm engagement with the tissue but in an alternate embodiment without the insulating member the helix may also be part of the electrode system if desired. Another feature of the present invention is that sealing means are provided in the opening in the electrode for preventing body fluids and tissue from reaching the proximal end of the electrode through the opening in the distal end.